Subject: [PATCH v2] pwm: i.MX: Avoid sample fifo overflow for i.MX pwm version2

From: [email-masked] (Liu Ying)
Date: Tue, 22 Apr 2014 16:48:44 +0800

Hi Thierry,

On 04/13/2014 03:46 PM, Shawn Guo wrote:
> On Thu, Apr 10, 2014 at 05:23:49PM +0800, Liu Ying wrote:
>> The i.MX pwm version2 is embedded in several i.MX SoCs, such
>> as i.MX27, i.MX51 and i.MX6SL.  There are four 16bit sample
>> fifos in this IP, each of which determines the duty period
>> of a PWM waveform in one full cycle.  The IP spec mentions
>> that we should not write a fourth sample because the fifo
>> will become full and trigger a fifo write error(FWE) which
>> will prevent the PWM from starting once it is enabled.  In
>> order to avoid any sample fifo overflow issue, this patch
>> does software reset to clear all the sample fifos in the
>> very beginning of the pwm configuration function.
>>
>> The fifo overflow issue can be reproduced by the following
>> commands on the i.MX6SL evk platform, assuming we use pwm2
>> for the debug LED which is driven by the pin HSIC_STROBE
>> and the maximal brightness is 255.
>> echo 0   > /sys/class/leds/user/brightness
>> echo 0   > /sys/class/leds/user/brightness
>> echo 0   > /sys/class/leds/user/brightness
>> echo 0   > /sys/class/leds/user/brightness
>> echo 255 > /sys/class/leds/user/brightness
>> Here, FWE happens(PWMSR register reads 0x58) and the LED
>> can not be lighten.
>>
>> Cc: Sascha Hauer <[email-masked]>
>> Cc: Shawn Guo <[email-masked]>
> 
> Acked-by: Shawn Guo <[email-masked]>
> 
>> Cc: Lothar Wa?mann <[email-masked]>
>> Cc: linux-pwm at vger.kernel.org
>> Cc: linux-arm-kernel at lists.infradead.org
>> Signed-off-by: Liu Ying <[email-masked]>
> 

I've got Shawn's ack on this patch.
If no objections, could you take it into your PWM tree?

Thanks.

-- 
Liu Ying